Live sphagnum is pretty much low maintenance in my experience. Just keep it moist, in bright light with good air circulation. It seems to prefer cooler conditions and might eventually die if kept in constant warm/greenhouse conditions.
I have a handfull growing in a clear plastic 4.5 inch pottery basket cup that I'm about to split transfer to bigger quarters.
I mist the moss a couple times a week with a spray bottle (distilled water of course).
Limit the amount of direct sunlight because too much will cause the tips to burn and turn brown or black. Air circulation will prevent algae growth which spells doom usually to sphagnum.